Conventionally, a gypsum-based board material such as a reinforce gypsum board, a normal hard gypsum board, a glass-fiber-nonwoven-fabric-containing gypsum plate, or a glass mat gypsum board, has an excellent performance in a fireproof property or fire resistance, a sound insulation property, a heat insulation property, a workability, an economical property, and the like, and hence, has been used widely.
A gypsum-based board material can be produced by molding a gypsum slurry and hardening the molded body of the gypsum slurry. Note that when a gypsum slurry is molded to form a molded body, a base paper for a board, a glass fiber nonwoven fabric or the like can be disposed on the surface of the molded body or in the vicinity of the surface, as needed.
A gypsum slurry can be prepared by a mixer or the like mixing and stirring calcined gypsum, water and, as needed, further various additive agents such as adhesive, and in some cases, by further adding foam so as to be at a predetermined specific gravity. Hence, a gypsum-based board material producing apparatus that is used to produce a gypsum-based board material includes a mixer (a mixing and stirring machine) that mixes raw materials of a gypsum slurry, a foaming apparatus that generates foam, and the like.
In recent years, a lightweight gypsum-based board material obtained by adding foam to a gypsum slurry and including voids derived from the foam is widely produced. In a case where such a gypsum-based board material obtained by adding foam to a gypsum slurry and including voids derived from the foam is produced, if the foam is not uniformly dispersed in the gypsum slurry and the foam is agglomerated and unevenly distributed, a local expansion, defect, or the like of the surface of the gypsum-based board material may occur.
Hence, various investigations have been made on mixers that enable to uniformly disperse foam in a gypsum slurry.
For example, Patent Document 1 discloses a mixer that includes: a flattened and circular housing provided with an annular wall on its periphery; a rotary disk located in the housing to rotate in a predetermined rotational direction; a slurry outlet port opening on the annular wall to discharge from the housing, gypsum slurry mixed in the housing; a hollow connector section with an open end connected to the slurry outlet port and another open end connected to a substantially vertical and cylindrical slurry delivery conduit; and a foam feeding port for feeding foam to the gypsum slurry. The foam feeding port is provided on the annular wall on an upstream side of the slurry outlet port in the rotational direction so as to feed the foam to the gypsum slurry immediately before the gypsum slurry enters the slurry outlet port, or provided on the hollow connector section so as to feed the foam to the gypsum slurry flowing in the hollow connector section.
Further, Patent Document 2 discloses a mixer that includes a mixing area for preparing gypsum slurry; a slurry delivery section for delivering the gypsum slurry from the mixing area; and a feeding port of foam or a foaming agent for feeding the gypsum slurry in the mixing area and/or the gypsum slurry in the slurry delivery section with the foam or foaming agent under pressure. The mixer is configured to supply the gypsum slurry with the foam mixed therein, to gypsum boards or a production line for gypsum boards. The feeding port has a partition member for dividing an ejecting region of the port, and the partition member divides the ejecting region into a plurality of openings that simultaneously supply the foam or foaming agent to the gypsum slurry.
In the disclosed Patent Documents 1 and 2 described above, a mixer and a foaming apparatus (a frothing apparatus) that supplies foam are directly connected by, for example, a pipe, and a method of controlling the amount of foam generated by the foaming apparatus to control the amount of foam added to a gypsum slurry is adopted.